The equation of state of a poly-E-caprolactam melt, PA-6, of molar mass M-n = 22kg/mol was investigated in a Gnomix apparatus (Gnomix Inc., Boulder, Colorado) between 300 and 560 K, and pressures up to 150 MPa. Cot-responding measurements were performed with addition of 1.6 wt% of montmorillonite exfoliated particles. Reductions in specific volume of about 1.0 and 1.4%, respectively, at 10 and 150 MPa, are observed. For the melt, excellent agreement between experiment and the results from lattice-hole theory is found for both systems. Addition of the nanoparticles reduced the hole (free volume) fraction by 14%. Evidently, the hole fraction is a sensitive indicator of structural changes. It is noteworthy that such a small quantity of added nanoparticles increases the tensile strength by about 14% and modulus by 26%, at a cost of reduction in the elongation at break by about 25%. For a treatment of the PNC, and as an approximation, our earlier model of a particulate composite was adopted. To calculate the binary interaction parameters it was assumed that: (1) the clay particles are in form of flat disks, 100 nm diameter and 1 nm thick; (2) the hard core segments of polymer and of solid occupy the same lattice volume, i.e. v(11)(*) = v(22)(*); (3) the energetic interactions of polymer with solid are given by the geometric average between the two self-interactions. These assumptions lead to the following results ('11' represents polymer-polymer, '22' represents clay-clay and '12' represents polymer-clay interactions): epsilon (*)(11) = 32.09; epsilon (*)(12) = 313.54 and epsilon (*)(22) = 3063 (kJ/mol) upsilon (*)(17) = 24.89; upsilon (*)(12) = 33.53 and upsilon (*)(22) = 24.89 (ml/mol).